A high-density information record can be regenerated on a rewritable optical disk. Therefore, the rewritable optical disk has been developed and put for sale on a commercial basis as a external storage device to a computer and an AV disk for images and voice. A groove (guide line) and a land (between grooves) are made on a high-density rewritable optical disk for tracking control of an optical beam. The well-known land-groove recording technology records and regenerates information on both lands and grooves.
As for an optical disk, a sector is a unit for recording information and is obtained by sectioning a disk of a record track for each amount of information. The header of each sector contains an ID signal preliminarily storing an address of the sector and various generally attributes. In the land-groove recording, an ID signal is provided between the adjacent land and groove so that the ID signal can be read from both land and groove. The Inventor and his associates have developed the ID detection circuit of an optical disk capable of correctly detecting the position and polarity of the ID signal (International Publication No. WO 97/39444).
In regenerating a signal of an optical disk, a very small signal, called a pit or a mark formed on a disk, equal to or smaller than 1 micron is irradiated by a spot light of a laser beam, and the intensity of a reflected light is read. Even if data is digitally stored, a regenerated waveform becomes an analog signal having an intermediate value by the optically or electrically low band passing frequency characteristic of a regeneration system. Therefore, an optical disk regeneration device requires an A/D conversion circuit for converting an analog regenerated signal into the original digital signal. The Inventor and his associates have already suggested the A/D conversion method for correctly digitizing a signal even if a regenerated signal of an optical disk indicates a fluctuation in amplitude and an asymmetric fluctuation (Japanese Laid-open Unexamined Patent Application No. 10-55621).
There are two major cases in which a regenerated signal of an optical disk is digitized. In the first case, a signal detected as an analog signal is to be returned to an original binary digital signal. In the second case, the quality of a regenerated signal is insufficient, and a true value is estimated from a signal before or after an erroneous point even if an error occurs during the regeneration. That is, to use the optimum decoding, an analog regenerated signal is converted into a multi-bit digital signal using an A/D converter, and then a digital signal process is performed. In the second case, an A/D converter normally having the resolution of 6 or more bits at a high conversion speed of a regeneration channel rate is required.
Among the optical disk devices, a device using a plurality of electric sum signals and difference signals detected by an optical detection unit requires an A/D converter for each of a sum signal and a difference signal. Even an optical disk device using only sum signals detects an offset at a DC level of a signal in the ID signal unit and a record signal unit. Especially, since a difference signal is detected with bi-polarity, a dynamic range of the circuit at the previous stage is required to A/D convert these signals as is. Additionally, the number of bits of the A/D converter should be increased. A multi-bit and high-speed A/D converter requires a special process in production, thereby causing a large power consumption as well as a costly system. The present invention has been developed to solve the above described problems, and aims at providing an optical disk signal processing method for digitizing a regenerated signal of a rewritable optical disk using a single A/D converter having the minimal number of bits, and an optical disk device thereby.